A new footprint thought to be a vital clue has now been ruled out in the desperate search for missing four-year-old August “Gus” Lamont.

It leaves investigators with little to no evidence and no clear direction for the search, which is now being wound down in the baffling case.

The little boy vanished from his family’s remote sheep station, about 40km south of Yunta in South Australia’s Mid North, about 5pm on Saturday, September 28.

He was last seen playing on a mound of dirt near the homestead. When his grandmother went to call him in just 30 minutes later, Gus was gone.

What followed was one of the largest search operations in South Australian history — involving police, SES volunteers and the Australian Army, scouring 60,000ha of harsh terrain by air and ground.

On September 30 search crews discovered a single footprint roughly 500m from where Gus was last seen.

On Tuesday, Deputy Commissioner Linda Williams said a second footprint found later has now been ruled out.

The investigation is now being led by the missing persons unit along with major crime.

The second print was found last week near a dam, with a “significant search” refocused on that area including specialist drone equipment used in investigation into the alleged murder of Julian Story.

“The print was subsequently not related to Gus,” Williams said

“On Friday and Saturday night a contingent of police also conducted a significant aerial search of the property using a special drone with infrared capabilities.

“This is the same technology that was used in the search in Port Lincoln for the remains of Julian Story.

“If any information comes that directs us to conduct further searches in specific areas we will be doing that in the coming weeks.

“We will never give up hope of finding Gus. There are further lines of enquiry being undertaken, and the family have continued to co-operate fully with police and have consented to every request that we have made of them thus far.”

The revelation has devastated search crews and the Lamont family, who have clung to hope through long days of uncertainty.

The earlier footprint found on September 30 remains the only clue to Gus’s disappearance but has not yet led to any further information or discoveries.

Former SES volunteer Jason O’Connell, who walked the property during the search alongside Gus’s father, said the case defies logic.

“My heart breaks for him,” O’Connell told 7NEWS on Monday.

“It’s been searched. Gus is not there.”

Despite extensive efforts, no trace of the child has been found — no clothing, no belongings, and no other signs of movement.

Assistant Commissioner Ian Parrott last week said police had made the tough call to scale back the search given it is unlikely Gus is alive.

“While we’ve all been hoping for a miracle, that miracle has not eventuated and, in the last 48 hours, despite the professional advice it being unlikely that Gus would have survived, we have maintained and in fact increased the effort to try to locate him and bring him (back to) his family,” he said.

“We’re confident that we’ve done absolutely everything we can to locate Gus within the search area but, despite our best efforts, we have not been able to locate him.”

While police have scaled back the search the investigation remains active.

Gus’s family describe him as a shy but adventurous child and say he was a good walker but had never left the property alone before.

He is described as Caucasian with long blond curly hair and was last seen wearing a grey sun hat, cobalt blue long-sleeve shirt with a yellow Minion on the front, light grey pants and boots.

Anyone with information is urged to contact police immediately.